1. Field of the Invention
The present invention relates to a method and an apparatus for a loading test of a pile using a self-repulsive force, i.e. the peripheral skin friction between the pile wall and the surrounding ground as the force required to cause the pile tip settlement, and more particularly to a method and an apparatus to carry out the loading test in which both a peripheral skin friction resistance and a tip end bearing capacity can be determined with ease and in a cost-effective manner.
2. Description of the Prior Arts
In general, there have been known three types of loading test methods, one type is to apply the load directly to a test pile, another type is to apply a load box or a load frame onto a test pile by means of a hydraulic jack, and a third type is to utilize a peripheral skin friction of the neighboring piles as the load causing the test pile settlement.
FIG. 1 illustrates a first method that a load is applied directly to a test pile 11. As shown in FIG. 1, a load box 12 is laid on an upper end of a test pile 11 filled with soil, sand, cement, wire, or given material. Balks 13 and I-shaped beams 14 are laid down sequentially under the load box 12, and then a loading test is carried out.
Referring to FIG. 2, a second method is carried out in such a manner that a load box or a load frame 22 supported by balks 23a and 23b is laid on a test pile 21, and I-beams 24 are disposed between the balks 23a and 23b. A test load more than expected maximum design load is applied to the load box 22. And then, a hydraulic jack 25 provided with a pressure gauge (not shown) is inserted between an upper end of the test pile 21 and the load box 22 to apply a load to the test pile 21 during a loading test.
Referring to FIG. 3, a third method for a loading test is carried out in such a manner that two reaction piles 33a and 33b or more are driven into the ground with a prescribed depth from the test pile 31. A reaction beam 34 having a stength enough to endure the axial force and the bending moment during the loading test is fixedly mounted on the upper ends of the reaction piles 33a and 33b. And then, a hydraulic jack 35 provided with a pressure gauge (not shown) is inserted between the upper end of the test pile 31 and the lower surface of the reaction beam 34 to apply a test load to the test pile 31 during the loading test.
However, in such conventional loading test methods, there have been raised some problems that it is difficult to use such methods because numerous structural components are required for the loading test and further they should be assembled one by one. Also, it needs prescribed time for curing the concrete in case that a concrete pile is used as a test pile. Furthermore, according to the conventional methods as mentioned above, only the combined forces i.e., summation of tip end bearing capacity and peripheral skin friction force can be measured. According to the known behavior of a pile, the majority of the applied load is supported by the peripheral skin friction force at the early stage of loading test, whereby it is impossible to apply the concept of the safety factor based on the actual load transferring mechanism of the pile in the conventional methods.